Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$209.94	6.369%	$223.3111	$223.31	$223.30	$223.30
Purchase #2	$114.48	7.507%	$123.074	$123.07	$123.05	$123.10
Purchase #3	$136.75	11.753%	$152.8222	$152.82	$152.80	$152.80
Purchase #4	$33.30	4.421%	$34.7722	$34.77	$34.75	$34.80
Purchase #5	$49.60	13.247%	$56.1705	$56.17	$56.15	$56.20
Purchase #6	$198.45	6.601%	$211.5497	$211.55	$211.55	$211.50
Purchase #7	$55.98	5.267%	$58.9285	$58.93	$58.95	$58.90
7 purchase totals =	$798.50		$860.6282	$860.62	$860.55	$860.60